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Of exceptions and aborts..

Note: This was originally posted on 21st January 2009 at http://forums.arm.com

The ARM reference manual specifies sometimes MOV PC,R14 and sometimes SUBS PC,R14, #4 for returning from exceptions. But they have not mentioned why. Can somebdy expain?
Also, when exactly does the PC get incremented? During the Fetch ?
And exactly when (Fetching / Decoding / Executing) does an exception get generated?
Does an undefined instruction get generated when the instruction is decoded or when it is executed?
What about Data and Prefetch aborts?

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Felix Varghese over 12 years ago +1 verified

Note: This was originally posted on 10th February 2009 at http://forums.arm.com The core is ARM7TDMI. Yes, they've given the return instruction for each exception. I was just looking for an explanation...

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0 Bhaveet Shah over 12 years ago

Note: This was originally posted on 9th February 2009 at http://forums.arm.com

Exactly. The value saved in LR seems to be inconsistent across exceptions. Which is the source of all my confusion!

You don't mention the core you are using, but the Technical Reference Manual for the core, I think, will tell you the appropriate instruction to use for each exception.

The documents can be found at:
[url="http://infocenter.arm.com/help/index.jsp"]http://infocenter.arm.com/help/index.jsp[/url]
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0 Bhaveet Shah over 12 years ago

Note: This was originally posted on 9th February 2009 at http://forums.arm.com

Exactly. The value saved in LR seems to be inconsistent across exceptions. Which is the source of all my confusion!

You don't mention the core you are using, but the Technical Reference Manual for the core, I think, will tell you the appropriate instruction to use for each exception.

The documents can be found at:
[url="http://infocenter.arm.com/help/index.jsp"]http://infocenter.arm.com/help/index.jsp[/url]
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